EF4124 Collision

I have been using an EF4124 switch for several weeks without any issues. Today, one of the users could not access the network. Upon inspecting the lights on the switch, I found the lights that corresponded to the user that was having problems to be flashing steadily, on-off-on-off. After consulting the online users guide I learned that this was indicative of a "collision." All other lights and users were functioning properly.I then tried several things...1. I restarted the switch. No change.2. Restarted the user's computer. No change.3. Restarted ALL machines connected to the switch AND the switch. No change.I am currently on a quest for a 100' cat5 cable to connect the computer directly to the switch with a different cable.